Do you sometimes find yourself losing focus on the job? Is your thinking a little fuzzy? It could be something in the air – and you and your co-workers may be the source.

We all know that excess carbon dioxide in the atmosphere is bad. It’s a greenhouse gas that contributes to global warming, though it has no immediate harmful effects on people in concentrations that occur outdoors. Until recently, experts believed that indoor carbon dioxide – which is emitted, for example, when people exhale – also was harmless except at extremely high levels of 5,000 parts per million or more.


New research, however, has prompted scientists to rethink this assumption.

Two studies, one published in 2012 and another last fall, suggest that indoor exposure to carbon dioxide can impair performance and decision-making. Although the research focused on workers, the findings pose troubling questions for people in many indoor environments, including schools, airplanes, autos and even homes.

“We spend 90 percent of our time indoors,” says Joseph Allen, an assistant professor of exposure assessment science at the Harvard T.H. Chan School of Public Health, lead author of the most recent study. “To get a sense of this, multiply your age by 0.9. That’s how many years you have spent indoors.”

Until now, research used CO2 measurements as a rough indicator of overall ventilation in buildings. Low ventilation rates allow concentrations of many pollutants to build up, which experts have blamed for illnesses. This new research, however, suggests that even carbon dioxide may be causing problems.

“Does this mean that kids in a crowded and poorly ventilated classroom have impaired decision-making? Does it mean that kids taking a high-stakes test like the SAT might be impaired? We don’t know,” says Mark Mendell, one of the authors of the 2012 study, which was conducted by the Department of Energy’s Lawrence Berkeley National Laboratory. “But the results for the first time raise this question.”


Outdoor concentrations of CO2 in the air are around 400 ppm. Building operators have long tried to keep levels below 1,000 – as an indication of adequate general ventilation, not because they had concerns about CO2 itself. But concentrations often exceed that, especially in crowded rooms with poor ventilation, Mendell says. Indoor levels can reach several thousand parts per million, according to the Berkeley scientists, with concentrations in classrooms occasionally exceeding 3,000 ppm.

Illnesses apparently related to tight, energy-efficient new buildings received increasing attention beginning in the 1970s, with the emergence of “sick building syndrome,” a cluster of symptoms that include headaches, respiratory symptoms and difficulty concentrating. Experts identified indoor air pollutants as the likely source, but they didn’t suspect that carbon dioxide was part of the problem.

The Harvard study, which also involved researchers from SUNY Upstate Medical Center and Syracuse University, used similar testing methods as the Berkeley study, but it monitored participants over a longer period. It confirmed the 2012 results.

The most obvious solution is to increase ventilation from the outside. But this will prove problematic if carbon dioxide levels continue to rise in the atmosphere. Also, it can be expensive: Outside air that comes inside must be warmed in the winter and cooled in the summer.

A recent paper by Allen and colleagues suggests that spending money to increase ventilation in office buildings would be very cost-effective for employers, estimating the cost of doubling indoor ventilation rates at $40 per person annually, against a productivity gain of $6,500 per person per year.

“The increased use of energy may be worthwhile, if it turns out to have important benefits for people in the workplace or the classroom, allowing them to think or perform better,” Mendell says.